The present invention relates to a leadframe, which includes leads with land electrodes functioning as external terminals and can replace a conventional leadframe with beam-like leads. The present invention also relates to a method for manufacturing a land-grid-array (LGA) resin-molded semiconductor device, in which a semiconductor chip is bonded onto the leadframe and the assembly is molded with a resin encapsulant.
In recent years, to catch up with rapidly advancing downsizing of electronic units, it has become increasingly necessary to assemble semiconductor components, like resin-molded semiconductor devices, at a higher and higher density. In response, sizes and thicknesses of semiconductor components have also been noticeably reduced. In parallel with this downsizing trend, the number of pins needed for a single electronic unit is also increasing day after day. To meet these demands, resin-molded semiconductor devices of a greatly shrunken size and with a drastically reduced thickness should now be assembled at an even higher density.
Hereinafter, a conventional leadframe for a resin-molded semiconductor device will be described.
FIG. 22 is a plan view illustrating the structure of a conventional leadframe. As illustrated in FIG. 22, the leadframe includes rectangular die pad 102, support leads 103, beam-like inner leads 104, outer leads 105 and tie bars 106, all of these members being provided inside a frame rail 101. The die pad 102 is used for mounting a semiconductor chip thereon. The support leads 103 support the die pad 102. The inner leads 104 will be electrically connected to the semiconductor chip with some connection members like metal fine wires. The outer leads 105 are joined to the respective inner leads 104 and to be connected to external terminals. And the tie bars 106 are provided for joining and fixing the outer leads 105 together and for preventing a resin encapsulant from overflowing during a resin molding process.
It should be noted that normally the leadframe does not consist of the single pattern shown in FIG. 22, but is made up of a plurality of such patterns, which are arranged and connected together both horizontally and vertically.
Next, a known resin-molded semiconductor device will be described. FIG. 23 is a cross-sectional view illustrating a resin-molded semiconductor device including the leadframe shown in FIG. 22.
As shown in FIG. 23, a semiconductor chip 107 has been bonded onto the die pad 102 of the leadframe and electrically connected to the inner leads 104 with metal fine wires 108. The semiconductor chip 107 on the die pad 102, the inner leads 104 and so on have been molded with a resin encapsulant 109. The outer leads 105 protrude from the side faces of the resin encapsulant 109 and have had their outer ends bent downward.
Next, a method for manufacturing the resin-molded semiconductor device will be described with reference to FIGS. 23 and 24. First, the semiconductor chip 107 is bonded, with an adhesive, onto the die pad 102 of the leadframe. This process step is called xe2x80x9cdie bondingxe2x80x9d. Next, the semiconductor chip 107 is connected to the respective inner ends of the inner leads 104 with the metal fine wires 108. This process step is called xe2x80x9cwire bondingxe2x80x9d. Subsequently, the semiconductor chip 107 and a portion of the leadframe inside the tie bars 106 (i.e., the inner leads 104 and so on) are molded with the resin encapsulant 109 such that the outer leads 105 protrude outward. This process step is called xe2x80x9cresin moldingxe2x80x9d. Finally, the tie bars 106 are cut off at the boundary between the tie bars 106 and the resin encapsulant 109 to separate the outer leads 105 from each other and remove the frame rail 101, and the respective outer ends of the outer leads 105 are bent. This process step is called xe2x80x9ctie bar cutting and bendingxe2x80x9d. In this manner, a resin-molded semiconductor device with the structure shown in FIG. 23 is completed. In FIG. 24, the dashed line indicates a region where the assembly is molded with the resin encapsulant 109.
As described above, the number of devices that should be integrated within a single semiconductor chip, or the number of pins per chip, has been on the rise these days. Thus, the number of outer leads should also be increased to catch up with this latest trend. That is to say, the number of inner leads, which are joined to the outer leads, should preferably be increased to cope with such an implementation. However, the width of the inner (or outer) lead has a processable limit. Thus, as the number of inner (or outer) leads is increased, the overall size of the leadframe and that of the resulting resin-molded semiconductor device also increase. In view of these states in the art, it is difficult to realize a downsized and thinned resin-molded semiconductor device. On the other hand, if only the number of inner leads is increased to cope with the rise in the number of pins needed for a semiconductor chip while using a leadframe of substantially the same size, then the width of a single inner lead should be further reduced. In such a case, however, it is much more difficult to perform various process steps for forming the leadframe, like etching, as originally designed.
Recently, face-bonded semiconductor devices, such as ball grid array (BGA) types and land grid array (LGA) types, are also available. In the semiconductor device of any of these types, first, a semiconductor chip is mounted onto a carrier (e.g., a printed wiring board) including external electrodes (e.g., ball electrodes or land electrodes) on its bottom. Next, the semiconductor chip is electrically connected to the external electrodes. And then the chip and its associated members are molded with a resin encapsulant on the upper surface of the carrier. The semiconductor device of this face-bonded type, which is mounted directly on a motherboard on the bottom, will be a mainstream product in the near future. Accordingly, it is now clear that the conventional leadframe and resin-molded semiconductor device using the leadframe will soon be out of date under the circumstances such as these.
Also, the conventional resin-molded semiconductor device includes outer leads protruding outward from the side faces of a resin encapsulant, and is supposed to be mounted onto a motherboard by bonding the outer leads to the electrodes on the motherboard. Accordingly, the conventional device cannot be mounted onto the board so reliably as the semiconductor devices of the BGA and LGA types. Nevertheless, the semiconductor devices of the BGA and LGA types are expensive, because these devices use a printed wiring board.
It is therefore an object of the present invention to provide a leadframe effectively applicable to a resin-molded semiconductor device, in which external terminals are arranged and exposed in lines on the bottom of the package with almost no resin bur left on.
It is another object of the present invention to provide a method for manufacturing the resin-molded semiconductor device using the leadframe.
An inventive leadframe includes a frame rail, a die pad, support leads and first and second groups of leads. The frame rail is made of a metal plate. The die pad is used for mounting a semiconductor chip thereon, and disposed approximately in a center region of an opening of the frame rail. One end of each of the support leads supports the die pad, while the other end thereof is connected to the frame rail. One end of each of the leads of the first group extends toward the die pad at least partially, while the other end thereof is connected to the frame rail. The bottom of each lead of the first group is used as a land electrode of a first group. One end of each of the leads of the second group extends toward the die pad and is closer to the die pad than the end of the lead of the first group is, while the other end thereof is connected to the frame rail. Part of the bottom of each lead of the second group is used as a land electrode of a second group. The first and second groups of land electrodes are arranged in two lines. At least part of each lead of the second group has been pressed down by half-cut pressworking such that the bottom of each land electrode of the second group is lower than that of each land electrode of the first group. That part of the lead of the second group is inclined downward.
If a resin-molded semiconductor device is formed using this leadframe, a land grid array (LGA) package can be obtained. That is to say, external terminals will be arranged in two lines on the bottom of this package. Specifically, the second group of land electrodes of land leads (i.e., the second group of leads) forms the inner one of the two, while the first group of land electrodes of leads (i.e., the first group of leads) forms the outer line. At least part of each lead of the second group has been pressed down by half-cut pressworking such that the bottom of each land electrode of the second group is lower than that of each land electrode of the first group. In addition, that part of the lead of the second group is inclined downward. Accordingly, when a pressure is applied to these leads, the bottom of the land electrode of the second group is forced into, and strongly adhered to, a seal sheet, and no resin encapsulant reaches the land electrode. As a result, a package, including external terminals with no resin bur left on, can be obtained.
In one embodiment of the present invention, that part of the lead of the second group is preferably inclined at an angle between 3 and 15 degrees with a principal surface of the leadframe.
An inventive method for manufacturing a resin-molded semiconductor device includes the step of a) preparing a leadframe. The leadframe includes a frame rail, a die pad, support leads and first and second groups of leads. The frame rail is made of a metal plate. The die pad is used for mounting a semiconductor chip thereon, and disposed approximately in a center region of an opening of the frame rail. One end of each of the support leads supports the die pad, while the other end thereof is connected to the frame rail. One end of each of the leads of the first group extends toward the die pad at least partially, while the other end thereof is connected to the frame rail. The bottom of each lead of the first group is used as a land electrode of a first group. One end of each of the leads of the second group extends toward the die pad and is closer to the die pad than the end of the lead of the first group is, while the other end thereof is connected to the frame rail. Part of the bottom of each lead of the second group is used as a land electrode of a second group. The first and second groups of land electrodes are arranged in two lines. At least part of each lead of the second group has been pressed down by half-cut pressworking such that the bottom of each land electrode of the second group is lower than that of each land electrode of the first group. And that part of the lead of the second group is inclined downward. The method further includes the steps of: b) bonding a semiconductor chip onto the die pad of the leadframe prepared; c) connecting electrode pads, which are formed on the principal surface of the semiconductor chip bonded to the die pad, to respective upper surfaces of the first and second groups of leads of the leadframe with metal fine wires; d) adhering a seal sheet to at least the bottoms of the die pad and the first and second groups of leads on the backside of the leadframe; e) molding an upper part of the leadframe, the semiconductor chip, the die pad and the metal fine wires together with a resin encapsulant, while applying a pressure to at least the ends of the first and second groups of leads to press the first and second groups of land electrodes against the seal sheet; and f) stripping the seal sheet from the leadframe after the step e) has been performed.
In this method, a resin-molded semiconductor device is formed by mounting a semiconductor chip on the leadframe, connecting the chip to the leads (whose bottoms will be land electrodes as external terminals) with metal fine wires and then molding these members together with a resin encapsulant. In this manner, a land grid array (LGA) package can be obtained. That is to say, external terminals will be arranged in two lines on the bottom of the resin-molded semiconductor device (or the package). Specifically, the second group of land electrodes of land leads (i.e., the second group of leads) forms the inner one of the two, while the first group of land electrodes of leads (i.e., the first group of lead) forms the outer line. Part of each lead of the second group has been pressed down by half-cut pressworking such that the bottom of the land electrode of the second group is lower than that of the land electrode of the first group. In addition, that part of the lead of the second group is inclined downward. Accordingly, when a pressure is applied to these leads, the bottoms of the land electrodes of the second group are forced into, and strongly adhered to, a seal sheet. That is to say, it is possible to prevent the leads of the second group from being lifted by the pressure applied during the injection of the resin encapsulant, and no resin encapsulant reaches the land electrodes. As a result, no resin bur will be left on the land electrodes of the second group.